The present invention is directed to medicaments and methods for treating (including alleviating and/or preventing) neuropsychiatric and/or neurological disorders, including chronic neurological disorders, such as neurological disorders mediated by or influenced by the thalamus. In particular, the present invention is directed to a medicament containing a botulinum toxin for treating a neuropsychiatric and/or a chronic neurological disorder by administering the botulinum toxin to a trigeminal nerve.
A neurological disorder is a central nervous system malfunction. The central nervous system includes the brain. The brain includes the dorsal end of the spinal cord, medulla, brain stem, pons, cerebellum, cerebrum and cortex.
Epilepsy
Epilepsy describes a condition in which a person has recurrent seizures due to a chronic, underlying process. A seizure is a paroxysmal event due to abnormal, excessive, hypersynchronous discharges from an aggregate of central nervous system neurons. Among the many causes of epilepsy, there are various epilepsy syndromes in which the clinical and pathologic characteristics are distinctive and suggest a specific underlying etiology. The prevalence of epilepsy has been estimated at 5 to 10 people per 1000 population. Severe, penetrating head trauma is associated with up to a 50% risk of leading to epilepsy. Other causes of epilepsy include stroke, infection and genetic susceptibility.
Antiepileptic drug therapy is the mainstay of treatment for most patients with epilepsy and a variety of drugs have been used. See e.g., Fauci, A. S. et al., Harrison's Principles of Internal Medicine, McGraw-Hill, 14th Edition (1998), page 2321. Twenty percent of patients with epilepsy are resistant to drug therapy despite efforts to find an effective combination of antiepileptic drugs. Surgery can then be an option. Video-EEC monitoring can be used to define the anatomic location of the seizure focus and to correlate the abnormal electrophysiologic activity with behavioral manifestations of the seizure. Routine scalp or scalp-sphenoidal recordings are usually sufficient for localization. A high resolution MRI scan is routinely used to identify structural lesions. Functional Imaging studies such as SPECT and PET are adjunctive tests that can help verify the localization of an apparent epileptogenic region with an anatomic abnormality.
Once the presumed location of the seizure onset is identified, additional studies, including neuropsychological testing and the intracarotid amobarbital test (Wada's test) can be used to assess language and memory localization and to determine the possible functional consequences of surgical removal of the epileptogenic region. In some cases, the exact extent of the resection to be undertaken can be determined by performing cortical mapping at the time of the surgical procedure. This involves electrophysiologic recordings and cortical stimulation of the awake patient to identify the extent of epileptiform disturbances and the function of the cortical regions in questions.
The most common surgical procedure for patients with temporal lobe epilepsy involves resection of the anteromedial temporal lobe (temporal lobotomy) or a more limited removal of the underlying hippocampus and amygdala. Focal seizures arising from extratemporal regions may be suppressed by a focal neocortical resection. Unfortunately, about 5% of patients can still develop clinically significant complications from surgery and about 30% of patients treated with temporal lobectomy will still have seizures.
Focal epilepsy can involve almost any part of the brain and usually results from a localized lesion of functional abnormality. One type of focal epilepsy is the psychomotor seizure. Current therapy includes use of an EEG to localize abnormal spiking waves originating in areas of organic brain disease that predispose to focal epileptic attacks, followed by surgical excision of the focus to prevent future attacks.
Chronic Pain
About one third of a population will experience chronic pain. In the United States chronic pain is the most common cause of long-term disability, partially or totally disabling about fifty million people. As the population ages, the number of people needing treatment for chronic pain from back disorders, degenerative joint diseases, rheumatologic conditions, fibromyalgia, visceral diseases, and cancers can be expected to increase.
Various events such as tissue injury can trigger pain signals to the brain. These electrical impulses are carried by thin unmyelinated nerves called nociceptors (C-fibers) that synapse with neurons in the dorsal horn of the spinal cord. From the dorsal horn, the pain signal is transmitted via the spinothalamic tract to the cerebral cortex, where it is perceived, localized and interpreted.
Chronic pain is not just a prolonged version of acute pain. As pain signals are repeatedly generated, neural pathways undergo physiochemical changes that make the central nervous system hypersensitive to the pain signals and resistant to antinociceptive input. This is called central sensitization.
Fibromyalgia is a chronic pain syndrome believed due to central sensitization. Characteristic symptoms of fibromyalgia include widespread pain, fatigue, sleep abnormalities and distress. Patients with fibromyalgia show psychophysical evidence of hyperalgesia, that is a heightened response to mechanical, thermal and electrical stimuli at various tender or trigger points. In fibromyalgia the sensation at these tender points is much more pronounced and patients have a decreased threshold of pain, responding to even minimal amounts of pressure. The Copenhagen Fibromyalgia Symposium defined fibromyalgia as a situation in which a patient has at least 11 of 18 specified tender points, present in all four quadrants of the body. Primary hyperalgesia develops in an area where injury to tissues has occurred and secondary hyperalgesia may be found in undamaged tissue. Peripheral and central abnormalities of nociception have also been described in fibromyalgia. Important nociceptor systems in the skin and muscles seem to undergo profound changes in patients with fibromyalgia through unknown mechanisms. They include sensitization of vanilloid receptor, acid-sensing ion channel receptors and purino-receptors. Tissue mediators of inflammation and nerve growth factors can excite these receptors and cause extensive changes in pain sensitivity, but patients with fibromyalgia lack consistent evidence for inflammatory soft tissue abnormalities. Therefore, recent investigations have focused on central nervous system mechanisms of pain in fibromyalgia. Treatments for fibromyalgia include steroid trigger point injections and medications such as tricyclic antidepressants, neurontin, and narcotics, but these all have negative side effects.
Post Stroke Pain
Pain can be debilitating and it is not uncommon to attribute widespread pain in the elderly to osteoarthritis within the spinal column structures and peripheral joints or to other musculoskeletal conditions. However, if pain is widespread and exhibits neuropathic features, such as dysaesthesias (poorly localized burning sensations that occur after a stimulus is applied), allodynia (triggered by stimuli which are not normally painful or pain which occurs other than in the area stimulated), hyperpathia (increased pain from normally painful stimuli) and hyperalgesia, it can be the result of a lesion or disorder such as Thalamic Pain Syndrome or Central Post-Stroke Pain (CPSP) originating from the central nervous system. The source of the pain is via the thalamus, the sensory processing center within the central nervous system.
A stroke is the result of loss of the blood supply to a part of the brain and can result in weakness and slurred speech. CPSP develops in about 8% of stroke patients, occurring within one to six months after the stroke. Common painkillers often have no effect on this pain, although some medications developed for epilepsy and depression may reduce pain after strokes. CPSP has also been treated with intravenous lidocaine or oral opioids, as well as amitriptyline, carbamazepine, tegretol and lamotrigine, but these medications have adverse side effects.
Regional Pain Syndrome
Complex Regional Pain Syndrome (CRPS) (also called Reflex Sympathetic Dystrophy Syndrome) is a chronic condition characterized by severe burning pain, pathological changes in bone and skin, excessive sweating, tissue swelling, and extreme sensitivity to touch. The syndrome is a nerve disorder that occurs at the site of an injury (most often to the arms or legs), and the disorder is unique in that it simultaneously affects the nerves, skin, muscles, blood vessels, and bones. It occurs especially after injuries from high-velocity impacts such as those from bullets or shrapnel. However, it may occur without apparent injury. CRPS is believed to be the result of dysfunction in the central or peripheral nervous systems. CRPS I is frequently triggered by tissue injury; the term describes all patients with the above symptoms but with no underlying nerve injury. Patients with CRPS II experience the same symptoms but their cases are dearly associated with a nerve injury. CRPS can strike at any age but is more common between the ages of 40 and 60, although the number of CRPS cases among adolescents and young adults is increasing. CRPS affects both men and women, although most experts agree that it is more common in young women. One visible sign of CRPS near the site of injury is warm, shiny red skin that later becomes cool and bluish.
The pain that patients report is out of proportion to the severity of the injury and gets worse, rather than better, over time. Eventually the joints become stiff from disuse, and the skin, muscles, and bone atrophy. The symptoms of CRPS vary in severity and duration, and early treatment often results in remission. If treatment is delayed, however, the disorder can quickly spread to the entire limb, and changes in bone and muscle may become irreversible. In 50 percent of CRPS cases, pain persists longer than 6 months and sometimes for years. Physicians use a variety of drugs to treat CRPS. Elevation of the extremity and physical therapy are also used to treat CRPS. Injection of a local anesthetic is usually the first step in treatment. TENS (transcutaneous electrical stimulation), a procedure in which brief pulses of electricity are applied to nerve endings under the skin, has helped some patients in relieving chronic pain. In some cases, surgical or chemical sympathectomy (interruption of the affected nerve(s) of the sympathetic nervous system) is performed to relieve pain, but these treatments may also destroy other sensations as well.
Phantom Limb Pain
Phantom limb pain is a conscious feeling of a painful limb, after the limb has been amputated. The brain creates a “whole body map” which remains intact even when a piece of the body no longer exists and phantom sensation or pain can result *when the brain sends persistent messages to limbs not there. Phantom pain or sensations can range in type and intensity. For example, a mild form might be experienced as a sharp, intermittent stabbing pain causing the limb to jerk in reaction to the pain. An example of a more severe type might be the feeling that the missing limb is being crushed. Usually phantom limb pain diminishes in frequency and intensity over time. For a small number of amputees, however, phantom limb pain can become chronic and debilitating because of the frequency and severity of the pain. Anesthetics such as lidocaine, marcaine, novocaine, pontocaine, and xylocaine are often used to prevent nerve cells from transmitting pain messages, thus relieving trigger points and reducing stump pain, but their effects are temporary. Anti-inflammatories (acetaminophen, aspirin, ibuprofen), antidepressants (Amitriptyline, Elavil, Pamelor, Paxil, Prozac, Zoloft), anticonvulsants (Tegretol, Neurontin) and narcotics (Codeine, Demerol, Morphine, Percodan, Percocet) are other medications also used to treat phantom pain, but these often have adverse side effects.
Demyelinating Disease Pain
Demyelinating diseases such as Multiple Sclerosis (MS), progressive multifocal leukoencephalopathy (PML), disseminated necrotizing leukoencephalopathy (DNL), acute disseminated encephalomyelitis, and Schilder disease are acquired chronic, inflammatory diseases that result in the destruction of myelin, the fatty insulation normally covering the nerve fibers that aids in the transmission of nerve impulses. Demyelination results in impaired transmission of action potentials along exposed axons, producing a multiplicity of neurological deficits, for example, sensory loss, weakness, visual loss, vertigo, incoordination, sphincter disturbances, and altered cognition. MS is usually characterized by a relapsing-remitting course in the early stages, with full or nearly full recovery, initially. Over time the disease enters an irreversible progressive phase of neurological deficit. Acute relapses are caused by inflammatory demyelination, while disease progression is thought to result from axonal loss. The disease process affects myelinated fibre tracts, such as the optic nerves and the white matter tracts of the brain and spinal cord. This may lead to a variety of symptoms, such as visual disturbances, bladder, bowel or sexual dysfunction, motor weakness and spasticity, sensory symptoms (numbness, dysaesthesia), cerebellar symptoms (tremor and ataxia), and other symptoms (fatigue, cognitive impairment and psychiatric complications). Therapies used to treat demyelinating disorders can be categorized into disease modifying therapies, drugs used in acute exacerbations and drugs used to treat disease complications. So far, no disease modifying therapy has been found that halts disease progression or improves neurological status.
For this reason, the mainstay of treatment remains symptomatic management. Current therapies predominantly influence the immune system and target the inflammatory processes that are involved in the disease pathology. Beta interferons (interferon beta-1b, known as Betaferon), glatiramer acetate (Copaxone) and mitoxantrone have been used for their immunomodulatory effects. These include inhibition of leukocyte proliferation and antigen presentation, inhibition of T-cell migration across the blood-brain barrier and modulation of cytokine production to produce an anti-inflammatory environment. Oral steroids, such as prednisolone, may be effective in shortening acute attacks of MS. Other potential therapies are undergoing clinical evaluation, including T-cell vaccination, interleukin 10, matrix metalloproteinase inhibitors, plasmapheresis, vitamin D, retinoic acid, ganciclovir, valaciclovir, bone marrow transplantation and autologous stem cell transplantation.
As indicated, various therapeutic treatments are available to as treatments for various neurological disorders, such as thalamically mediated disorders. However, these therapeutic treatments have several adverse side-effects. These side-effects may be attributed to the fact that the pharmaceutical agents are typically administered systemically, and therefore, the agents have a relatively non-specific action with respect to the various biological systems of the patient. For example, administration of benzodiazepines may result in sedation and muscle relaxation. In addition, tolerance may develop to these drugs, as well as withdrawal seizures may develop. Current therapeutic strategies also require consistent and repeated administration of the agents to achieve the desired effects.
Neuropsychiatric Disorders
A neuropsychiatric disorder is a neurological disturbance that is typically labeled according to which of the four mental faculties is affected. For example, one group of neuropsychiatric disorders includes disorders of thinking and cognition, such as schizophrenia and delirium. A second group of neuropsychiatric disorders includes disorders of mood, such as affective disorders and anxiety. A third group of neuropsychiatric disorders includes disorders of social behavior, such as character defects and personality disorders. And a fourth group of neuropsychiatric disorders includes disorders of learning, memory, and intelligence, such as mental retardation and dementia. Accordingly, neuropsychiatric disorders encompass schizophrenia, delirium, Alzheimer's disease, depression, mania, attention deficit disorders, drug addiction, dementia, agitation, apathy, anxiety, psychoses, personality disorders, bipolar disorders, obsessive-compulsive disorders, eating disorders, post-traumatic stress disorders, irritability, and disinhibition.
Schizophrenia
Schizophrenia is a disorder that affects about one percent of the world population. Three general symptoms of schizophrenia are often referred to as positive symptoms, negative symptoms, and disorganized symptoms. Positive symptoms can include delusions (abnormal beliefs), hallucinations (abnormal perceptions), and disorganized thinking. The hallucinations of schizophrenia can be auditory, visual, olfactory, or tactile. Disorganized thinking can manifest itself in schizophrenic patients by disjointed speech and the inability to maintain logical thought processes. Negative symptoms can represent the absence of normal behavior. Negative symptoms include emotional flatness or lack of expression and can be characterized by social withdrawal, reduced energy, reduced motivation, and reduced activity. Catatonia can also be associated with negative symptoms of schizophrenia. The symptoms of schizophrenia should continuously persist for a duration of about six months in order for the patient to be diagnosed as schizophrenic. Based on the types of symptoms a patient reveals, schizophrenia can be categorized into subtypes including catatonic schizophrenia, paranoid schizophrenia, and disorganized schizophrenia.
The brains of schizophrenic patients are often characterized by enlarged lateral ventricles, which can be associated with a reduction of the hippocampus and an enhancement in the size of the basal ganglia. Schizophrenic patients can also have enlarged third ventricles and widening of sulci. These anatomical characterizations point to a reduction in cortical tissue.
Although the cause of schizophrenia is not precisely known, there are several hypotheses. One hypothesis is that schizophrenia is associated with increased dopamine activity within the cortical and limbic areas of the brain. This hypothesis is supported by the therapeutic effects achieved by antipsychotic drugs that block certain dopamine receptors. In addition, amphetamine use can be associated with schizophrenia-like psychotic symptoms, and it is known that amphetamines act on dopamine receptors.
Examples of antipsychotic drugs that may be used to treat schizophrenic patients include phenothiazines, such as chlorpromazine and triflupromazine; thioxanthenes, such as chlorprothixene; fluphenazine; butyrophenones, such as haloperidol; loxapine; mesoridazine; molindone; quetiapine; thiothixene; trifluoperazine; perphenazine; thioridazine; risperidone; dibenzodiazepines, such as clozapine; and olanzapine. Although these agents may relieve the symptoms of schizophrenia, their administration can result in undesirable side effects including Parkinson's disease-like symptoms (tremor, muscle rigidity, loss of facial expression); dystonia; restlessness; tardive dyskinesia; weight gain; skin problems; dry mouth; constipation; blurred vision; drowsiness; slurred speech and agranulocytosis.
Antipsychotic drugs are believed to primarily act on dopamine receptors with a particular affinity for the D2, D3, and D4 receptors. It is believed that the D3 and D4 receptors may have a higher affinity for certain antipsychotics, such as clozapine, as compared to the others. The brains of schizophrenic patients appear to have increased numbers of D2 receptors in the caudate nucleus, the nucleus accumbens (ventral striatum), and the olfactory tubercle.
Dopamine neurons may be organized into four major subsystems: the tuberoinfundibular system; the nigrostriatal system; the mesolimbic system; and the mesocortical system. The tuberoinfundibular dopaminergic system originates in cell bodies of the arcuate nucleus of the hypothalamus and projects to the pituitary stalk. This system may be involved in secondary neuroendocrine abnormalities in schizophrenia. The nigrostriatal dopaminergic system originates in the substantia nigra and projects primarily to the putamen and the caudate nucleus. The mesolimbic dopaminergic system originates in the ventral tegmental area and projects to the mesial component of the limbic system, which includes the nucleus accumbens, the nuclei of the stria terminalis, parts of the amygdala and hippocampus, the lateral septal nuclei, and the mesial frontal, anterior cingulate, and entorhinal cortex. The nucleus accumbens is a convergence site from the amygdala, hippocampus, entorhinal area, anterior cingulate area, and parts of the temporal lobe. Thus, the mesolimbic dopaminergic projection can modulate and transform information conveyed from the nucleus accumbens to the septum, hypothalamus, anterior cingulate area, and frontal lobes, and overactive modulation of the nucleus accumbens output to these areas can contribute to positive symptoms associated with schizophrenia. The mesocortical dopaminergic system originates in the ventral tegmental area and projects to the neocortex and heavily to the prefrontal cortex. This component may be important in the negative symptoms of schizophrenia.
The ventral tegmental area, which is the source of origination of the dopaminergic input to the nucleus accumbens, receives a cholinergic input from the pedunculopontine nuclei of the brainstem. The pedunculopontine nucleus provides an excitatory cholinergic input to the ventral tegmental area (Clarke et al., Innervation of substantia nigra neurons by cholinergic afferents from the pedunculopontine nucleus in the rat. Neuroanatomical and electrophysiological evidence, Neuroscience, 23:1011-1019, 1987). It has been reported that schizophrenic patients have an increased number of cholinergic neurons in the pedunculopontine nuclei (Garcia-Rill et al., Mesopontine neurons in schizophrenia, Neuroscience, 66(2):321-335, 1995). However, these results were not confirmed in one study (German et al., Mesopontine cholinergic and non-cholinergic neurons in schizophrenia, Neuroscience, 94(1):33-38, 1999).
Mania
Mania is a sustained form of euphoria that affects millions of people in the United States who suffer from depression. Manic episodes can be characterized by an elevated, expansive, or irritable mood lasting several days, and is often accompanied by other symptoms, such as, overactivity, overtalkativeness, social intrusiveness, increased energy, pressure of ideas, grandiosity, distractibility, decreased need for sleep, and recklessness. Manic patients can also experience delusions and hallucinations.
Depressive disorders can involve serotonergic and noradrenergic neuronal systems based on current therapeutic regimes that target serotonin and noradrenalin receptors. Serotonergic pathways originate from the raphe nuclei of the brain stem, and noradrenergic pathways originate from the locus coeruleus. Decreasing the electrical activity of neurons in the locus coeruleus can be associated with the effects mediated by depression medications.
Mania may results from an imbalance in certain chemical messengers within the brain. It has been proposed that mania is attributed to a decline in acetylcholine. A decline in acetylcholine may result in a relatively greater level of norepinephrine. Administering phosphatidyl choline has been reported to alleviate the symptoms of mania.
Anxiety
Anxiety disorders may affect between approximately ten to thirty percent of the population, and can be characterized by frequent occurrence of symptoms of fear including arousal, restlessness, heightened responsiveness, sweating, racing heart, increased blood pressure, dry mouth, a desire to run or escape, and avoidance behavior. Generalized anxiety persists for several months, and is associated with motor tension (trembling, twitching, muscle aches, restlessness); autonomic hyperactivity (shortness of breath, palpitations, increased heart rate, sweating, cold hands), and vigilance and scanning (feeling on edge, exaggerated startle response, difficult in concentrating).
Benzodiazepines, which enhance the inhibitory effects of the gamma aminobutyric acid (GABA) type A receptor, are frequently used to treat anxiety. Buspirone is another effective anxiety treatment.
Alzheimer's Disease
Alzheimer's disease is a degenerative brain disorder characterized by cognitive and noncognitive neuropsychiatric symptoms, which accounts for approximately 60% of all cases of dementia for patients over 65 years old. Psychiatric symptoms are common in Alzheimer's disease, with psychosis (hallucinations and delusions) present in approximately fifty percent of affected patients. Similar to schizophrenia, positive psychotic symptoms are common in Alzheimer's disease. Delusions typically occur more frequently than hallucinations. Alzheimer's patients may also exhibit negative symptoms, such as disengagement, apathy, diminished emotional responsiveness, loss of volition, and decreased initiative.
Alzheimers disease patients may also exhibit enlargement of both lateral and third ventricles as well as atrophy of temporal structures.
It is possible that the psychotic symptoms of Alzheimer's disease involve a shift in the concentration of dopamine or acetylcholine, which may augment a dopaminergic/cholinergic balance, thereby resulting in psychotic behavior. For example, it has been proposed that an increased dopamine release may be responsible for the positive symptoms of schizophrenia. This may result in a positive disruption of the dopaminergic/cholinergic balance. In Alzheimer's disease, the reduction in cholinergic neurons effectively reduces acetylcholine release resulting in a negative disruption of the dopaminergic/cholinergic balance. Indeed, antipsychotic agents that are used to relieve psychosis of schizophrenia are also useful in alleviating psychosis in Alzheimer's patients.
Several of the symptoms associated with neuropsychiatric disorders appear to be, at least in part, attributed to hyperexcitability (i.e. sensitization to afferent input from peripheral nerves) of neurons within the brain. This interpretation is supported by the pharmacology associated with current therapeutic treatments. For example, many of the antipsychotic treatments are directed to interfering with binding of dopamine to dopamine receptors, as discussed above. Similarly, mania and anxiety are often treated with benzodiazepines, which enhance the inhibitory effects of GABA-mediated inhibition. U.S. Pat. No. 6,306,403 discloses intracranial administration of a botulinum toxin to treat various movement disorders. Additionally, it is known that stereotactic procedures can be used to administer a pharmaceutical to a discrete brain area to successfully alleviate a parkinsonian tremor. See e.g. Pahapill P. A., et al., Tremor arrest with thalamic microinjections of muscimol in patients with essential tremor, Ann Neur 46(2); 249-252 (1999).
However, current therapeutic treatments result in several adverse side-effects. These side-effects may be attributed to the fact that the pharmaceutical agents are typically administered systemically, and therefore, the agents have a relatively non-specific action with respect to the various biological systems of the patient. For example, administration of benzodiazepines may result in sedation and muscle relaxation. In addition, tolerance may develop to these drugs, as well as withdrawal seizures may develop. Current therapeutic strategies also require consistent and repeated administration of the agents to achieve the desired effects.
Trigeminal Nerve
The trigeminal nerve has three major branches, a number of smaller branches and is the great sensory nerve of the head and neck, carrying touch, temperature, pain, and proprioception (position sense) signals from the face and scalp to the brainstem. Trigeminal sensory fibers originate in the skin, course toward the trigeminal ganglion (a sensory nerve cell body), pass through the trigeminal ganglion, and travel within the trigeminal nerve to the sensory nucleus of the trigeminal nerve located in the brainstem.
The three major branches of the trigeminal nerve are the ophthalmic (V1, sensory), maxillary (V2, sensory) and mandibular (V3, motor and sensory) branches. The large trigeminal sensory root and smaller trigeminal motor root leave the brainstem at the midlateral surface of pons. The sensory root terminates in the largest of the cranial nerve nuclei which extends from the pons all the way down into the second cervical level of the spinal cord. The sensory root joins the trigeminal or semilunar ganglion between the layers of the dura mater in a depression on the floor of the middle crania fossa. The trigeminal motor root originates from cells located in the masticator motor nucleus of trigeminal nerve located in the midpons of the brainstem. The motor root passes through the trigeminal ganglion and combines with the corresponding sensory root to become the mandibular nerve. It is distributed to the muscles of mastication, the mylohyoid muscle and the anterior belly of the digastric. The three sensory branches of the trigeminal nerve emanate from the ganglia to form the three branches of the trigeminal nerve. The ophthalmic and maxillary branches travel in the wall of the cavernous sinus just prior to leaving the cranium. The ophthalmic branch travels through the superior orbital fissure and passes through the orbit to reach the skin of the forehead and top of the head. The maxillary nerve enters the cranium through the foramen rotundum via the pterygopalatine fossa. Its sensory branches reach the pterygopalatine fossa via the inferior orbital fissure (face, cheek and upper teeth) and pterygopalatine canal (soft and hard palate, nasal cavity and pharynx). There are also meningeal sensory branches that enter the trigeminal ganglion within the cranium. The sensory part of the mandibular nerve is composed of branches that carry general sensory information from the mucous membranes of the mouth and cheek, anterior two-thirds of the tongue, lower teeth, skin of the lower jaw, side of the head and scalp and meninges of the anterior and middle cranial fossae.
The sensory nuclei of the trigeminal nerve are located within the brainstem, in the dorsolateral pons. The mesencephalic tract and the motor nucleus of the trigeminal nerve lie more medially. The superior cerebellar peduncle lies posteriorly. It is continuous inferiorly with the spinal nucleus of the trigeminal nerve that extends into the medulla. Superiorly, the sensory nuclei on each side are continuous with the mesencephalic nucleus.
Importantly, the sensory nuclei of the trigeminal nerve receive afferent (sensory input) fibres from: (1) the trigeminal nerve ophthalmic division (e.g. general sensation from supraorbital area, cornea, iris, ethmoid sinuses), (2) trigeminal nerve maxillary division (e.g. sensation from temple, cheek, oral cavity, upper pharynx), and (3) trigeminal nerve mandibular division (e.g. sensation from middle cranial fossa, inner cheek, anterior two thirds of the tongue, chin), (4) facial nerve (e.g. general sensation from external auditory meatus), (5) glossopharyngeal nerve (e.g. general sensation from middle ear, tonsils, oropharynx, posterior one third of the tongue), (6) vagus nerve (auricular, meningeal, internal laryngeal and recurrent laryngeal branches).
Thus, primary neurons in the trigeminal ganglion synapse on the main sensory trigeminal nucleus and on the spinal trigeminal nucleus in the brainstem. The spinal nucleus of the trigeminal system extends to the upper cervical spine, where connections with cervical dermatomes exist. These dermatomes are innervated by the cervical plexus, which has sensory branches from C1 to C4. The trigeminal nerve also innervates stretch receptors in the muscles of mastication. The cell bodies of these neurons are in the mesencephalic trigeminal nucleus in the midbrain and pons).
As indicated by FIG. 1, the ascending (afferent) second order trigeminal neurons from the main sensory trigeminal nucleus, and the ascending second order neurons from the spinal trigeminal nucleus ascend and synapse in the thalamus. Projections from the thalamus are to the facial representation of the sensory cortex. Central projections from the mesencephalic trigeminal nucleus are to the motor cortex. Thalamic projections to the sensory cortex follow a somatotopic organization. The hand and face have disproportionately greater representation on a homunculus map. This body map is not static, but dynamically controlled by the pattern of use, with increased use leading to increased cortical representation. Notably, the primary somatosensory cortex in the post central gyrus, receives input from the thalamus, and projects to the secondary somatic sensory cortex in the parietal operculum. There are also efferent connections from the sensory cortex to the motor cortex. Notably, the trigeminal nerve is a very large nerve and 28% of the sensory cortex is devoted to it alone.
Botulinum Toxin
The genus Clostridium has more than one hundred and twenty seven species, grouped according to their morphology and functions. The anaerobic, gram positive bacterium Clostridium botulinum produces a potent polypeptide neurotoxin, botulinum toxin, which causes a neuroparalytic illness in humans and animals referred to as botulism. The spores of Clostridium botulinum are found in soil and can grow in improperly sterilized and sealed food containers of home based canneries, which are the cause of many of the cases of botulism. The effects of botulism typically appear 18 to 36 hours after eating the foodstuffs infected with a Clostridium botulinum culture or spores. The botulinum toxin can apparently pass unattenuated through the lining of the gut and shows a high affinity for cholinergic motor neurons. Symptoms of botulinum toxin intoxication can progress from difficulty walking, swallowing and speaking to paralysis of the respiratory muscles and death.
Botulinum toxin type A is the most lethal natural biological agent known to man. About 50 picograms of a commercially available botulinum toxin type A (purified neurotoxin complex, Available from Allergan, Inc., of Irvine, Calif. under the tradename BOTOX® in 100 unit vials) is a LD50 in mice (i.e. 1 unit). One unit of BOTOX® contains about 50 picograms (about 56 attomoles) of botulinum toxin type A complex. Interestingly, on a molar basis, botulinum toxin type A is about 1.8 billion times more lethal than diphtheria, about 600 million times more lethal than sodium cyanide, about 30 million times more lethal than cobra toxin and about 12 million times more lethal than cholera. Singh, Critical Aspects of Bacterial Protein Toxins, pages 63-84 (chapter 4) of Natural Toxins II, edited by B. R. Singh et al., Plenum Press, New York (1976) (where the stated LD50 of botulinum toxin type A of 0.3 ng equals 1 U is corrected for the fact that about 0.05 ng of BOTOX® equals 1 unit). One unit (U) of botulinum toxin is defined as the LD50 upon intraperitoneal injection into female Swiss Webster mice weighing 18 to 20 grams each.
Seven generally immunologically distinct botulinum toxins have been characterized, these being respectively botulinum toxin serotypes A, B, C1, D, E, F and G each of which is distinguished by neutralization with type-specific antibodies. The different serotypes of botulinum toxin vary in the animal species that they affect and in the severity and duration of the paralysis they evoke. For example, it has been determined that botulinum toxin type A is 500 times more potent, as measured 1o by the rate of paralysis produced in the rat, than is botulinum toxin type B. Additionally, botulinum toxin type B has been determined to be non-toxic in primates at a dose of 480 U/kg which is about 12 times the primate LD50 for botulinum toxin type A. Moyer E et al., Botulinum Toxin Type B: Experimental and Clinical Experience, being chapter 6, pages 71-85 of “Therapy With Botulinum Toxin”, edited by Jankovic, J. et al. (1994), Marcel Dekker, Inc. Botulinum toxin apparently binds with high affinity to cholinergic motor neurons, is translocated into the neuron and blocks the release of acetylcholine. Additional uptake can take place through low affinity receptors, as well as by phagocytosis and pinocytosis.
Regardless of serotype, the molecular mechanism of toxin intoxication appears to be similar and to involve at least three steps or stages. In the first step of the process, the toxin binds to the presynaptic membrane of the target neuron through a specific interaction between the heavy chain (the H chain or HC), and a cell surface receptor. The receptor is thought to be different for each type of botulinum toxin and for tetanus toxin. The carboxyl end segment of the HC appears to be important for targeting of the botulinum toxin to the cell surface.
In the second step, the botulinum toxin crosses the plasma membrane of the target cell. The botulinum toxin is first engulfed by the cell through receptor-mediated endocytosis, and an endosome containing the botulinum toxin is formed. The toxin then escapes the endosome into the cytoplasm of the cell. This step is thought to be mediated by the amino end segment of the HC, the HN, which triggers a conformational change of the toxin in response to a pH of about 5.5 or lower. Endosomes are known to possess a proton pump which decreases intra-endosomal pH. The conformational shift exposes hydrophobic residues in the toxin, which permits the botulinum toxin to embed itself in the endosomal membrane. The botulinum toxin (or at least the light chain of the botulinum) then translocates through the endosomal membrane into the cytoplasm.
The last step of the mechanism of botulinum toxin activity appears to involve reduction of the disulfide bond joining the heavy chain, H chain, and the light chain, L chain. The entire toxic activity of botulinum and tetanus toxins is contained in the L chain of the holotoxin; the L chain is a zinc (Zn++) endopeptidase which selectively cleaves proteins essential for recognition and docking of neurotransmitter-containing vesicles with the cytoplasmic surface of the plasma membrane, and fusion of the vesicles with the plasma membrane. Tetanus neurotoxin, botulinum toxin types B, D, F and G cause degradation of synaptobrevin (also called vesicle-associated membrane protein (VAMP)), a synaptosomal membrane protein. Most of the VAMP present at the cytoplasmic surface of the synaptic vesicle is removed as a result of any one of these cleavage events. Botulinum toxin serotype A and E cleave SNAP-25. Botulinum toxin serotype C1 was originally thought to cleave syntaxin, but was found to cleave syntaxin and SNAP-25. Each of the botulinum toxins specifically cleaves a different bond, except botulinum toxin type B (and tetanus toxin) which cleave the same bond. Each of these cleavages block the process of vesicle-membrane docking, thereby preventing exocytosis of vesicle content.
Botulinum toxins have been used in clinical settings for the treatment of neuromuscular disorders characterized by hyperactive skeletal muscles (i.e. motor disorders). In 1989, a botulinum toxin type A complex was approved by the U.S. Food and Drug Administration for the treatment of blepharospasm, strabismus and hemifacial spasm. Subsequently, a botulinum toxin type A was also approved by the FDA for the treatment of cervical dystonia and for the treatment of glabellar lines, and a botulinum toxin type B was approved for the treatment of cervical dystonia. Non-type A botulinum toxin serotypes apparently have a lower potency and/or a shorter duration of activity as compared to botulinum toxin type A. Clinical effects of peripheral intramuscular botulinum toxin type A are usually seen within one week of injection. The typical duration of symptomatic relief from a single intramuscular injection of botulinum toxin type A averages about three months, although significantly longer periods of therapeutic activity have been reported.
Although all the botulinum toxins serotypes apparently inhibit release of the neurotransmitter acetylcholine at the neuromuscular junction, they do so by affecting different neurosecretory proteins and/or cleaving these proteins at different sites. For example, botulinum types A and E both cleave the 25 kiloDalton (kD) synaptosomal associated protein (SNAP-25), but they target different amino acid sequences within this protein. Botulinum toxin types B, D, F and G act on vesicle-associated protein (VAMP, also called synaptobrevin), with each serotype cleaving the protein at a different site. Finally, botulinum toxin type C1 has been shown to cleave both syntaxin and SNAP-25. These differences in mechanism of action may affect the relative potency and/or duration of action of the various botulinum toxin serotypes. Apparently, a substrate for a botulinum toxin can be found in a variety of different cell types. See e.g. Biochem J 1; 339 (pt 1):159-65:1999, and Mov Disord, 10(3):376:1995 (pancreatic islet B cells contains at least SNAP-25 and synaptobrevin).
The molecular weight of the botulinum toxin protein molecule, for all seven of the known botulinum toxin serotypes, is about 150 kD. Interestingly, the botulinum toxins are released by Clostridial bacterium as complexes comprising the 150 kD botulinum toxin protein molecule along with associated non-toxin proteins. Thus, the botulinum toxin type A complex can be produced by Clostridial bacterium as 900 kD, 500 kD and 300 kD forms. Botulinum toxin types B and C1 is apparently produced as only a 700 kD or 500 kD complex. Botulinum toxin type D is produced as both 300 kD and 500 kD complexes. Finally, botulinum toxin types E and F are produced as only approximately 300 kD complexes. The complexes (i.e. molecular weight greater than about 150 kD) are believed to contain a non-toxin hemagglutinin proteins and a non-toxin and non-toxic nonhemagglutinin protein. These two non-toxin proteins (which along with the botulinum toxin molecule comprise the relevant neurotoxin complex) may act to provide stability against denaturation to the botulinum toxin molecule and protection against digestive acids when a botulinum toxin is ingested. Additionally, it is possible that the larger (greater than about 150 kD molecular weight) botulinum toxin complexes may result in a slower rate of diffusion of the botulinum toxin away from a site of intramuscular injection of a botulinum toxin complex.
In vitro studies have indicated that botulinum toxin inhibits potassium cation induced release of both acetylcholine and norepinephrine from primary cell cultures of brainstem tissue. Additionally, it has been reported that botulinum toxin inhibits the evoked release of both glycine and glutamate in primary cultures of spinal cord neurons and that in brain synaptosome preparations botulinum toxin inhibits the release of each of the neurotransmitters acetylcholine, dopamine, norepinephrine (Habermann E., et al., Tetanus Toxin and Botulinum A and C Neurotoxins Inhibit Noradrenaline Release From Cultured Mouse Brain, J Neurochem 51(2); 522-527:1988) CGRP, substance P and glutamate (Sanchez-Prieto, J., et al., Botulinum Toxin A Blocks Glutamate Exocytosis From Guinea Pig Cerebral Cortical Synaptosomes, Eur J. Biochem 165; 675-681:1897. Thus, when adequate concentrations are used, stimulus-evoked release of most neurotransmitters can be blocked by botulinum toxin. See e.g. Pearce, L. B., Pharmacologic Characterization of Botulinum Toxin For Basic Science and Medicine, Toxicon 35(9); 1373-1412 at 1393; Bigalke H., et al., Botulinum A Neurotoxin Inhibits Non-Cholinergic Synaptic Transmission in Mouse Spinal Cord Neurons in Culture, Brain Research 360; 318-324:1985; Habermann E., Inhibition by Tetanus and Botulinum A Toxin of the release of [3H]Noradrenaline and [3H]GABA From Rat Brain Homogenate, Experientia 44; 224-226:1988, Bigalke H., et al., Tetanus Toxin and Botulinum A Toxin Inhibit Release and Uptake of Various Transmitters, as Studied with Particulate Preparations From Rat Brain and Spinal Cord, Naunyn-Schmiedeberg's Arch Pharmacol 316; 244-251:1981, and; Jankovic J. et al., Therapy With Botulinum Toxin, Marcel Dekker, Inc., (1994), page 5.
Botulinum toxin type A can be obtained by establishing and growing cultures of Clostridium botulinum in a fermenter and then harvesting and purifying the fermented mixture in accordance with known procedures. All the botulinum toxin serotypes are initially synthesized as inactive single chain proteins which must be cleaved or nicked by proteases to become neuroactive. The bacterial strains that make botulinum toxin serotypes A and G possess endogenous proteases and serotypes A and G can therefore be recovered from bacterial cultures in predominantly their active form. In contrast, botulinum toxin serotypes C1, D and E are synthesized by nonproteolytic strains and are therefore typically unactivated when recovered from culture. Serotypes B and F are produced by both proteolytic and nonproteolytic strains and therefore can be recovered in either the active or inactive form. However, even the proteolytic strains that produce, for example, the botulinum toxin type B serotype only cleave a portion of the toxin produced. The exact proportion of nicked to unnicked molecules depends on the length of incubation and the temperature of the culture. Therefore, a certain percentage of any preparation of, for example, the botulinum toxin type B toxin is likely to be inactive, possibly accounting for the known significantly lower potency of botulinum toxin type B as compared to botulinum toxin type A. The presence of inactive botulinum toxin molecules in a clinical preparation will contribute to the overall protein load of the preparation, which has been linked to increased antigenicity, without contributing to its clinical efficacy. Additionally, it is known that botulinum toxin type B has, upon intramuscular injection, a shorter duration of activity and is also less potent than botulinum toxin type A at the same dose level.
High quality crystalline botulinum toxin type A can be produced from the Hall A strain of Clostridium botulinum with characteristics of ≥3×107 U/mg, an A260/A278 of less than 0.60 and a distinct pattern of banding on gel electrophoresis. The known Shantz process can be used to obtain crystalline botulinum toxin type A, as set forth in Shantz, E. J., et al, Properties and use of Botulinum toxin and Other Microbial Neurotoxins in Medicine, Microbiol Rev. 56; 80-99:1992. Generally, the botulinum toxin type A complex can be isolated and purified from an anaerobic fermentation by cultivating Clostridium botulinum type A in a suitable medium. The known process can also be used, upon separation out of the non-toxin proteins, to obtain pure botulinum toxins, such as for example: purified botulinum toxin type A with an approximately 150 kD molecular weight with a specific potency of 1-2×108 LD50 U/mg or greater; purified botulinum toxin type B with an approximately 156 kD molecular weight with a specific potency of 1-2×108 LD50 U/mg or greater, and; purified botulinum toxin type F with an approximately 155 kD molecular weight with a specific potency of 1-2×107 LD50 U/mg or greater.
Botulinum toxins and/or botulinum toxin complexes can be obtained from List Biological Laboratories, Inc., Campbell, Calif.; the Centre for Applied Microbiology and Research, Porton Down, U.K.; Wako (Osaka, Japan), Metabiologics (Madison, Wis.) as well as from Sigma Chemicals of St Louis, Mo. Pure botulinum toxin can also be used to prepare a pharmaceutical composition.
As with enzymes generally, the biological activities of the botulinum toxins (which are intracellular peptidases) is dependant, at least in part, upon their three dimensional conformation. Thus, botulinum toxin type A is detoxified by heat, various chemicals surface stretching and surface drying. Additionally, it is known that dilution of a botulinum toxin complex obtained by the known culturing, fermentation and purification to the much, much lower toxin concentrations used for pharmaceutical composition formulation results in rapid detoxification of the toxin unless a suitable stabilizing agent is present. Dilution of the toxin from milligram quantities to a solution containing nanograms per milliliter presents significant difficulties because of the rapid loss of specific toxicity upon such great dilution. Since the botulinum toxin may be used months or years after the toxin containing pharmaceutical composition is formulated, the toxin can be stabilized with a stabilizing agent such as albumin and gelatin.
A commercially available botulinum toxin containing pharmaceutical composition is sold under the trademark BOTOX® (available from Allergan, Inc., of Irvine, Calif.). BOTOX® consists of a purified botulinum toxin type A complex, albumin and sodium chloride packaged in sterile, vacuum-dried form. The botulinum toxin type A is made from a culture of the Hall strain of Clostridium botulinum grown in a medium containing N-Z amine and yeast extract. The botulinum toxin type A complex is purified from the culture solution by a series of acid precipitations to a crystalline complex consisting of the active high molecular weight toxin protein and an associated hemagglutinin protein. The crystalline complex is re-dissolved in a solution containing saline and albumin and sterile filtered (0.2 microns) prior to vacuum-drying. The vacuum-dried product is stored in a freezer at or below −5° C. BOTOX® can be reconstituted with sterile, non-preserved saline prior to intramuscular injection. Each vial of BOTOX® contains about 100 units (U) of Clostridium botulinum toxin type A purified neurotoxin complex, 0.5 milligrams of human serum albumin and 0.9 milligrams of sodium chloride in a sterile, vacuum-dried form without a preservative.
To reconstitute vacuum-dried BOTOX®, sterile normal saline without a preservative; (0.9% Sodium Chloride Injection) is used by drawing up the proper amount of diluent in the appropriate size syringe. Since BOTOX® may be denatured by bubbling or similar violent agitation, the diluent is gently injected into the vial. For sterility reasons BOTOX® is preferably administered within four hours after the vial is removed from the freezer and reconstituted. During these four hours, reconstituted BOTOX® can be stored in a refrigerator at about 2° C. to about 8° C. Reconstituted, refrigerated BOTOX® has been reported to retain its potency for at least about two weeks. Neurology, 48:249-53:1997.
It has been reported that botulinum toxin type A has been used in clinical settings as follows:
(1) about 75-125 units of BOTOX® per intramuscular injection (multiple muscles) to treat cervical dystonia;
(2) 5-10 units of BOTOX® per intramuscular injection to treat glabellar lines (brow furrows) (5 units injected intramuscularly into the procerus muscle and 10 units injected intramuscularly into each corrugator supercilii muscle);
(3) about 30-80 units of BOTOX® to treat constipation by intrasphincter injection of the puborectalis muscle;
(4) about 1-5 units per muscle of intramuscularly injected BOTOX® to treat blepharospasm by injecting the lateral pre-tarsal orbicularis oculi muscle of the upper lid and the lateral pre-tarsal orbicularis oculi of the lower lid.
(5) to treat strabismus, extraocular muscles have been injected intramuscularly with between about 1-5 units of BOTOX®, the amount injected varying based upon both the size of the muscle to be injected and the extent of muscle paralysis desired (i.e. amount of diopter correction desired).(6) to treat upper limb spasticity following stroke by intramuscular injections of BOTOX® into five different upper limb flexor muscles, as follows:(a) flexor digitorum profundus: 7.5 U to 30 U(b) flexor digitorum sublimis: 7.5 U to 30 U(c) flexor carpi ulnaris: 10 U to 40 U(d) flexor carpi radialis: 15 U to 60 U(e) biceps brachii: 50 U to 200 U. Each of the five indicated muscles has been injected at the same treatment session, so that the patient receives from 90 U to 360 U of upper limb flexor muscle BOTOX® by intramuscular injection at each treatment session.(7) to treat migraine, pericranial injected (injected symmetrically into glabellar, frontalis and temporalis muscles) injection of 25 U of BOTOX® has showed significant benefit as a prophylactic treatment of migraine compared to vehicle as measured by decreased measures of migraine frequency, maximal severity, associated vomiting and acute medication use over the three month period following the 25 U injection.
It is known that botulinum toxin type A can have an efficacy for up to 12 months (European J. Neurology 6 (Suppl 4): S111-S1150:1999), and in some circumstances for as long as 27 months, when used to treat glands, such as in the treatment of hyperhidrosis. See e.g. Bushara K., Botulinum toxin and rhinorrhea, Otolaryngol Head Neck Surg 1996; 114(3):507, and The Laryngoscope 109:1344-1346:1999. However, the usual duration of an intramuscular injection of Botox® is typically about 3 to 4 months.
The success of botulinum toxin type A to treat a variety of clinical conditions has led to interest in other botulinum toxin serotypes. Two commercially available botulinum type A preparations for use in humans are BOTOX® available from Allergan, Inc., of Irvine, Calif., and Dysport® available from Beaufour Ipsen, Porton Down, England. A botulinum toxin type B preparation (MyoBloc®) is available from Elan Pharmaceuticals of San Francisco, Calif.
In addition to having pharmacologic actions at the peripheral location, botulinum toxins may also have inhibitory effects in the central nervous system. Work by Weigand et al, Naunyn-Schmiedeberg's Arch. Pharmacol. 1976; 292, 161-165, and Habermann, Naunyn-Schmiedeberg's Arch. Pharmacol. 1974; 281, 47-56 showed that botulinum toxin is able to ascend to the spinal area by retrograde transport. As such, a botulinum toxin injected at a peripheral location, for example intramuscularly, may be retrograde transported to the spinal cord.
U.S. Pat. No. 5,989,545 discloses that a modified clostridial neurotoxin or fragment thereof, preferably a botulinum toxin, chemically conjugated or recombinantly fused to a particular targeting moiety can be used to treat pain by administration of the agent to the spinal cord.
It has been reported that use of a botulinum toxin to treat various spasmodic muscle conditions can result in reduced depression and anxiety, as the muscle spasm is reduced. Murry T., et al., Spasmodic dysphonia; emotional status and botulinum toxin treatment, Arch Otolaryngol 1994 March; 120(3): 310-316; Jahanshahi M., et al., Psychological functioning before and after treatment of torticollis with botulinum toxin, J Neurol Neurosurg Psychiatry 1992; 55(3): 229-231. Additionally, German patent application DE 101 50 415 A1 discusses intramuscular injection of a botulinum toxin to treat depression and related affective disorders.
A botulinum toxin has also been proposed for or has been used to treat skin wounds (U.S. Pat. No. 6,447,787), various autonomic nerve dysfunctions (U.S. Pat. No. 5,766,605), tension headache, (U.S. Pat. No. 6,458,365), migraine headache pain (U.S. Pat. No. 5,714,468), sinus headache (U.S. patent application serial number 429069), post-operative pain and visceral pain (U.S. Pat. No. 6,464,986), neuralgia pain (U.S. patent application Ser. No. 630,587), hair growth and hair retention (U.S. Pat. No. 6,299,893), dental related ailments (U.S. provisional patent application Ser. No. 60/418,789), fibromyalgia (U.S. Pat. No. 6,623,742), various skin disorders (U.S. patent application Ser. No. 10/731,973), motion sickness (U.S. patent application Ser. No. 752,869), psoriasis and dermatitis (U.S. Pat. No. 5,670,484), injured muscles (U.S. Pat. No. 6,423,319) various cancers (U.S. Pat. No. 6,139,845), smooth muscle disorders (U.S. Pat. No. 5,437,291), down turned mouth corners (U.S. Pat. No. 6,358,917), nerve entrapment syndromes (U.S. patent application 2003 0224019), various impulse disorders (U.S. patent application Ser. No. 423,380), acne (WO 03/011333) and neurogenic inflammation (U.S. Pat. No. 6,063,768). Controlled release toxin implants are known (see e.g. U.S. Pat. Nos. 6,306,423 and 6,312,708) as is transdermal botulinum toxin administration (U.S. patent application Ser. No. 10/194,805).
Botulinum toxin type A has been used to treat epilepsia partialis continua, a type of focal motor epilepsy. Bhattacharya K., et al., Novel uses of botulinum toxin type A: two case reports, Mov Disord 2000; 15(Suppl 2):51-52.
It is known that a botulinum toxin can be used to: weaken the chewing or biting muscle of the mouth so that self inflicted wounds and resulting ulcers can heal (Payne M., et al, Botulinum toxin as a novel treatment for self mutilation in Lesch-Nyhan syndrome, Ann Neurol 2002 September; 52(3 Supp 1):S157); permit healing of benign cystic lesions or tumors (Blugerman G., et al., Multiple eccrine hidrocystomas: A new therapeutic option with botulinum toxin, Dermatol Surg 2003 May; 29(5):557-9); treat anal fissure (Jost W., Ten years' experience with botulinum toxin in anal fissure, Int J Colorectal Dis 2002 September; 17(5):298-302, and; treat certain types of atopic dermatitis (Heckmann M., et al., Botulinum toxin type A injection in the treatment of lichen simplex: An open pilot study, J Am Acad Dermatol 2002 April; 46(4):617-9).
Additionally, a botulinum toxin may have an effect to reduce induced inflammatory pain in a rat formalin model. Aoki K., et al, Mechanisms of the antinociceptive effect of subcutaneous Botox: Inhibition of peripheral and central nociceptive processing, Cephalalgia 2003 September; 23(7):649. Furthermore, it has been reported that botulinum toxin nerve blockage can cause a reduction of epidermal thickness. Li Y, et al., Sensory and motor denervation influences epidermal thickness in rat foot glabrous skin, Exp Neurol 1997; 147:452-462 (see page 459). Finally, it is known to administer a botulinum toxin to the foot to treat excessive foot sweating (Katsambas A., et al., Cutaneous diseases of the foot: Unapproved treatments, Clin Dermatol 2002 November-December; 20(6):689-699; Sevim, S., et al., Botulinum toxin—A therapy for palmar and plantar hyperhidrosis, Acta Neurol Belg 2002 December; 102(4):167-70), spastic toes (Suputtitada, A., Local botulinum toxin type A injections in the treatment of spastic toes, Am J Phys Med Rehabil 2002 October; 81(10):770-5), idiopathic toe walking (Tacks, L., et al., Idiopathic toe walking: Treatment with botulinum toxin A injection, Dev Med Child Neurol 2002; 44(Suppl 91):6), and foot dystonia (Rogers J., et al., Injections of botulinum toxin A in foot dystonia, Neurology 1993 April; 43(4 Suppl 2)).
Tetanus toxin, as wells as derivatives (i.e. with a non-native targeting moiety), fragments, hybrids and chimeras thereof can also have therapeutic utility. The tetanus toxin bears many similarities to the botulinum toxins. Thus, both the tetanus toxin and the botulinum toxins are polypeptides made by closely related species of Clostridium (Clostridium tetani and Clostridium botulinum, respectively). Additionally, both the tetanus toxin and the botulinum toxins are dichain proteins composed of a light chain (molecular weight about 50 kD) covalently bound by a single disulfide bond to a heavy chain (molecular weight about 100 kD). Hence, the molecular weight of tetanus toxin and of each of the seven botulinum toxins (non-complexed) is about 150 kD. Furthermore, for both the tetanus toxin and the botulinum toxins, the light chain bears the domain which exhibits intracellular biological (protease) activity, while the heavy chain comprises the receptor binding (immunogenic) and cell membrane translocational domains.
Further, both the tetanus toxin and the botulinum toxins exhibit a high, specific affinity for ganglioside receptors on the surface of presynaptic cholinergic neurons. Receptor mediated endocytosis of tetanus toxin by peripheral cholinergic neurons results in retrograde axonal transport, blocking of the release of inhibitory neurotransmitters from central synapses and a spastic paralysis. Contrarily, receptor mediated endocytosis of botulinum toxin by peripheral cholinergic neurons results in little if any retrograde transport, inhibition of acetylcholine exocytosis from the intoxicated peripheral motor neurons and a flaccid paralysis.
Finally, the tetanus toxin and the botulinum toxins resemble each other in both biosynthesis and molecular architecture. Thus, there is an overall 34% identity between the protein sequences of tetanus toxin and botulinum toxin type A, and a sequence identity as high as 62% for some functional domains. Binz T. et al., The Complete Sequence of Botulinum Neurotoxin Type A and Comparison with Other Clostridial Neurotoxins, J Biological Chemistry 265(16); 9153-9158:1990.
Acetylcholine
Typically only a single type of small molecule neurotransmitter is released by each type of neuron in the mammalian nervous system, although there is evidence which suggests that several neuromodulators can be released by the same neuron. The neurotransmitter acetylcholine is secreted by neurons in many areas of the brain, but specifically by the large pyramidal cells of the motor cortex, by several different neurons in the basal ganglia, by the motor neurons that innervate the skeletal muscles, by the preganglionic neurons of the autonomic nervous system (both sympathetic and parasympathetic), by the bag 1 fibers of the muscle spindle fiber, by the postganglionic neurons of the parasympathetic nervous system, and by some of the postganglionic neurons of the sympathetic nervous system. Essentially, only the postganglionic sympathetic nerve fibers to the sweat glands, the piloerector muscles and a few blood vessels are cholinergic as most of the postganglionic neurons of the sympathetic nervous system secret the neurotransmitter norepinephrine. In most instances acetylcholine has an excitatory effect. However, acetylcholine is known to have inhibitory effects at some of the peripheral parasympathetic nerve endings, such as inhibition of heart rate by the vagal nerve.
The efferent signals of the autonomic nervous system are transmitted to the body through either the sympathetic nervous system or the parasympathetic nervous system. The preganglionic neurons of the sympathetic nervous system extend from preganglionic sympathetic neuron cell bodies located in the intermediolateral horn of the spinal cord. The preganglionic sympathetic nerve fibers, extending from the cell body, synapse with postganglionic neurons located in either a paravertebral sympathetic ganglion or in a prevertebral ganglion. Since, the preganglionic neurons of both the sympathetic and parasympathetic nervous system are cholinergic, application of acetylcholine to the ganglia will excite both sympathetic and parasympathetic postganglionic neurons.
Acetylcholine activates two types of receptors, muscarinic and nicotinic receptors. The muscarinic receptors are found in all effector cells stimulated by the postganglionic, neurons of the parasympathetic nervous system as well as in those stimulated by the postganglionic cholinergic neurons of the sympathetic nervous system. The nicotinic receptors are found in the adrenal medulla, as well as within the autonomic ganglia, that is on the cell surface of the postganglionic neuron at the synapse between the preganglionic and postganglionic neurons of both the sympathetic and parasympathetic systems. Nicotinic receptors are also found in many nonautonomic nerve endings, for example in the membranes of skeletal muscle fibers at the neuromuscular junction.
Acetylcholine is released from cholinergic neurons when small, clear, intracellular vesicles fuse with the presynaptic neuronal cell membrane. A wide variety of non-neuronal secretory cells, such as, adrenal medulla (as well as the PC12 cell line) and pancreatic islet cells release catecholamines and parathyroid hormone, respectively, from large dense-core vesicles. The PC12 cell line is a clone of rat pheochromocytoma cells extensively used as a tissue culture model for studies of sympathoadrenal development. Botulinum toxin inhibits the release of both types of compounds from both types of cells in vitro, permeabilized (as by electroporation) or by direct injection of the toxin into the denervated cell. Botulinum toxin is also known to block release of the neurotransmitter glutamate from cortical synaptosomes cell cultures.
A neuromuscular junction is formed in skeletal muscle by the proximity of axons to muscle cells. A signal transmitted through the nervous system results in an action potential at the terminal axon, with activation of ion channels and resulting release of the neurotransmitter acetylcholine from intraneuronal synaptic vesicles, for example at the motor endplate of the neuromuscular junction. The acetylcholine crosses the extracellular space to bind with acetylcholine receptor proteins on the surface of the muscle end plate. Once sufficient binding has occurred, an action potential of the muscle cell causes specific membrane ion channel changes, resulting in muscle cell contraction. The acetylcholine is then released from the muscle cells and metabolized by cholinesterases in the extracellular space. The metabolites are recycled back into the terminal axon for reprocessing into further acetylcholine.
What is needed therefore is a method for effectively treating neuropsychiatric and/or neurological disorders, such as a thalamically mediated disorders, by peripheral administration of a pharmaceutical.